Adventures Among Ants - Mark W. Moffett [79]
While most major human civilizations have undertaken full-time defense of large tracts of land, until modern times borderlands were often fluid, reflecting not wars but decisions about current utility. For example, in fallow months the Mongols would abandon the pastures on which they grazed livestock during fruitful seasons.18 Our modern fixed territories are similar to the “absolute territories” of weaver ants, where space is defended all the time, and reflect the close packing of their populous societies. In a rainforest filled with ants, no colony can afford to relinquish its territory. “Free space is the enemy of true warfare,” writes the military theorist Robert O’Connell, and the stranglehold weaver ants maintain over their crowded canopy dominions gives credence to this view.19 The only territorial changes typical of a weaver ant society are shifts in battle lines with a neighbor or changing levels of worker activity on the forest floor—which weaver ants treat as a less essential, and often seasonal, part of their home range. They abandon it, much as the Mongols did their marginal grazing lands, when conditions are too wet or too dry. Their territoriality reflects this: when certain competing ant species move on the ground beneath weaver ant–occupied trees, for example, the weaver ants merely avoid them, but when the same ants dare to ascend the weavers’ tree, the invasion elicits a massive fighting response.20
The versatility of weaver ant communication systems is without parallel among the ants, but that’s no surprise given the nature of their operations. There are parallels here between the size of a superorganism and the size of an organism. To handle logistical issues within their bodies, big creatures often require more-elaborate organs, including brains and hormone-secreting endocrine glands, than do tiny ones, which sometimes get by with no neurons or hormones at all. Large body size can also mean a capacity for behavioral innovations, which are most common in vertebrates with big brains, such as chimpanzees, who use sticks to catch ants.21 The massed workers in a large ant weaver society may be similarly adept at solving problems or achieving goals, including keeping track of territorial space, enemies, prey, and good sites for leaf nests.
For humans, it’s thought that when communities and their institutions, from the government to the marketplace, evolve beyond a threshold size, the potential arises for more complex social mechanisms.22 Weaver ants, with their intricate transport and communication systems, conform to this expectation of emergent complexity with greater social size.23
HUNTING, GATHERING, AND ANIMAL HUSBANDRY
Weaver ants forage everywhere, while incessantly protecting every leaf, twig, and branch. With ready access to other weaver ant foragers in the canopy and to a surfeit of ants in nearby nests, the workers are able to handle unpredictably scattered prey and enemy incursions. If a dense army ant raid is like a powerful net trawling a limited area in a narrow swath, the workers spread across a weaver ant territory act as an immense, and only slightly weaker, fixed net. The space that weaver ants occupy is so huge that the influx of prey into their territories is enormous. Indeed, a mature colony processes millions of victims each year.24 Each worker typically stands at one spot, using something like the sit-and-wait strategy of the bumpy Proatta ants I watched in Singapore, but with greater effectiveness. They keep their jaws open and body erect, pivoting occasionally. Unlike the sightless driver ants, weavers are so visually acute that they can follow the flight paths of tiny fruit flies and snatch them out of the air before they alight.
Even when a weaver ant is capable of subduing an insect on her own, capture of all but the smallest prey is almost always a group enterprise.25 Attracted in part by the struggle, in part by the sternal gland pheromone, weavers use the spread-eagle